Silicone "bouncing putty" has been widely marketed over the past twenty years. This material, which derives its name from its putty-like consistency and bouncing property, has a unique combination of physical attributes. They are generally plastic and free-flowing under low stress but shatter like glass under a suddenly applied stress. They can be rolled into a ball and bounced, and when bounced, they rebound further and faster than ordinary rubber balls.
A silicone putty exhibiting elasticity or "bounce" is described in U.S. Pat. No. 2,541,581 which issued to James G. E. Wright on Feb. 13, 1951. According to Wright, bouncing putties may be made by heating a mixture of dimethyl silicone and a boron compound, followed by the addition of inorganic fillers and zinc hydroxide and "kneading" the resultant mixture until a putty-like consistency is attained.
In the hitherto known or conventional methods of making silly-putty, a polysiloxane oil, a boron compound and fillers are charged to a so-called "dough mixer" and heated to a temperature of about 350.degree. F. After the mixture attains this temperature, it is "cooked" for several hours and during the cooking operation a nitrogen blanket is spread over the mixture to prevent the volatiles which are produced during this operation from burning or exploding. When the cooking is completed (usually within about 10 hours), the mix is cooled until it can be handled and worked safely and comfortably, and then evacuated from the mixer. Plasticizers are then added and worked into the mix as desired.
When made in conventional mixers by the presently known methods, a high percentage of the putty is rejected because of inadequate or insufficient bounce of the resulting putty. The principal reason for the inferior bounce of the putty made in the presently used conventional mixers, e.g., dough mixers, is that the volatiles produced during heating of the mixture are not expelled from the system. Therefore, and in general, approximately 30 to 50 percent of the bouncing putty produced have inferior or inadequate strength and rebound capability.
Accordingly, it is an object of this invention to make a bouncing putty which has a high degree of rebound, i.e., "bounce" while retaining the other desirable properties and attributes of the putty.
It is also an object of this invention to make bouncing putty by a method which minimizes the amount of the rejected material.
It is a further object of this invention to make such putty-like composition by a method which permits expulsion of the volatiles produced during the process.